Various transparent materials have been conventionally used as optical waveguides for optical total internal reflection. Examples of such optical waveguides are optical fibers and sheets of acrylic or glass.
However, total internal reflection can be “frustrated” on an image-wise basis by engraving marks in the surface of the optical medium (optical waveguide) so that the internally reflecting light partially externally refracts and escapes the optical waveguide. Engraving marks in the surface of the optical medium enables the production of a variety of optical signs where the image appears to “hover” in space.
FIG. 1 shows a conventional edge lit sign wherein a piece of acrylic 10 is edge lit with a light source (LEDS) 20. The light is internally reflected within the acrylic 10 except where the light encounters engraved regions (11, 12, and 13) that introduce interface angles (as illustrated in FIG. 2), between acrylic 10 and air. The interface angles, formed by the engraving process, “frustrate” internal reflection and allow light to escape the acrylic 10 at these points (11, 12, and 13). The effect of this type of imaging is striking since the light seems to originate in the engraved images (11, 12, and 13).
As illustrated in FIG. 2, light 25 from a light source is totally reflected within the optical waveguide 10 until it encounters an engraved section 11. At the engraved section 11, a portion of the light 25 is frustrated and is refracted out of the optical waveguide as escaped light 27. This refraction at the engraved section 11 causes the light to appear to originate in the engraved image section 11.
However, there are disadvantages to this approach. First, since the color of the light is the color of the illumination source, the images tend to be monochromatic.
This limitation can be overcome, as illustrated in FIG. 3, by using several pieces of acrylic or optical waveguides (10, 16, and 18), each etched with an image (11, 125, and 135) associated with a specific color and illuminated with that a light source (20, 22, and 24) of that color.
This solution is complicated and requires several pieces of etched optical waveguides and several sources of edge illumination.
A second disadvantage is that laser engraving machines draw lines, not rasterized halftone patterns. Thus, laser engraving limits the engravings to line art and cannot provide shading and/or density levels that halftoning can provide.
A third disadvantage of utilizing laser engraving is that once the image is engraved, the optical waveguide cannot be re-used for other images.
Thus, it is desirable to provide a system or process that enables the emanation of an image having multiple distinct colors from a surface of single optical waveguide.
It is further desirable to provide a system or process that that enables the emanation of an image with variable shading or variable light density levels from a surface of single optical waveguide.
It is also desirable to provide a system or process that enables the emanation of an image having multiple distinct colors from a surface of single optical waveguide while maintaining the re-usability of the optical waveguide to emanation other images.
It is additionally desirable to provide a system or process that that enables the emanation of an image with variable shading or variable light density levels from a surface of single optical waveguide while maintaining the re-usability of the optical waveguide to emanation other images.